Have iomux_update_events be a no-op if the events didn't change

include/ucore/iomux.h

@@ -105,20 +105,11 @@ int iomux_register_fd(struct IOMux *mux, struct IOMuxFD *fd);
  */
 int iomux_unregister_fd(struct IOMux *mux, struct IOMuxFD *fd);
 
-/** Updates the events to watch for in fd->what
+/** Updates the events to watch for 
+ *
  * @return 0 on success, an errno value on error
  */
-int iomux_update_events(struct IOMux *mux, struct IOMuxFD *fd);
-
-
-/**
- * Convenience macro for setting the new event
- */
-#define iomux_set_event(mux, fd, what_)\
-({\
-    (fd)->what = (what_);\
-    iomux_update_events((mux), (fd));\
-})
+int iomux_update_events(struct IOMux *mux, struct IOMuxFD *fd, unsigned int what);
 
 /**
  * Convenience macro for clearing the new event
@@ -126,15 +117,14 @@ int iomux_update_events(struct IOMux *mux, struct IOMuxFD *fd);
 #define iomux_clear_event(mux, fd, what_)\
 ({\
     (fd)->what &= ~(what_);\
-    iomux_update_events((mux), (fd));\
+    iomux_update_events((mux), (fd), (fd)->what & ~(what_));\
 })
 /**
  * Convenience macro for adding the new event to the existing events
  */
 #define iomux_add_event(mux, fd, what_)\
 ({\
-    (fd)->what &= (what_);\
-    iomux_update_events((mux), (fd));\
+    iomux_update_events((mux), (fd), (fd)->what | (what_));\
 })
 
 /** @return a UCTimer instance tied to this mux.

src/iomux_impl.c

@@ -130,13 +130,21 @@ int iomux_unregister_fd(struct IOMux *mux, struct IOMuxFD *fd)
     return mux->unregister_fd_impl(mux, fd);
 }
 
-int iomux_update_events(struct IOMux *mux, struct IOMuxFD *fd)
+int iomux_update_events(struct IOMux *mux, struct IOMuxFD *fd, unsigned int what)
 {
+    int rc;
     assert(mux != NULL);
     assert(fd != NULL);
     assert(fd->callback != NULL);
     assert(fd->fd >= 0);
-    return mux->update_events_impl(mux, fd);
+    
+    if (fd->what != what) {
+        mux->update_events_impl(mux, fd);
+    } else {
+        rc = 0;
+    }
+
+    return rc;
 }
 
 struct UCoreClock *iomux_get_clock(struct IOMux *mux)